Legal Question in Administrative Law in California

You are probably dealing with an "interim" ordinance, based on the 10 month, 15 day extension mentioned.

I have not found any requirement in the Government Code, nor is any mentioned in the California Municipal Law Handbook, that urgency ordinances expire. The main difference between urgency ordinances and other ordinances is in the method of adoption and earliest possible effective date. So, I'd say the purpose of an urgency ordinance is to place a law on the books as quickly as possible to address an emergency. The emergency must be described in the ordinance itself or the ordinance is subject to challenge.

I'd also say the city council doesn't have to replace urgency ordinances, and that they don't automatically expire simply because they were passed as such.

Please distinguish ordinances passed as "interim" measures, for example, under Government Code section 65858, which are or can be a subspecies of urgency measures. These, as "interim" measures, do have a limit on how long they can be in effect, and are only available for certain purposes relating to zoning restrictions. If the ordinance you have in mind deals with zoning, you might want to look up California Government Code section 65858 on the Internet and read it, and perhaps also section 65090.